To stay alive, living beings realize metabolisms.
Here are the 5 things a living being needs :
- light,
- air : oxygen and CO2,
- Water,
- Food,
- An appropriate temperature.
Experience
There are 10 000 species of known bacterias. They are very different and pocess caracteristics which let them exist before others.
Bacterias can resist veyy high pressure and help to create an atmosphere. They can be the sign of probable life on a planet
To conclude, bacterias are the first elements to live on a planet and let life develop if the conditions are good enough.
All these hypothesis lead to the creation of amino acids and micro-organisms.
Life would have appeared 3,5 billion years ago. Under the form of bacterias. Bacterias are at the origin of much complex organisms such as plants or animals.
bacterias have 2 forms :
- coccis
- bacillis
This theory was studied by the scientists Stanley Miller and Harold Urey. It explains that from some gases, (H2O, H2, NH3 and CH4) we can synthesize all the organic molecules in our lifetime (such as the amino acids)
The terrestrial prebiotic soup
This theory is based on the study of the solar system’s fragments, such as meteorites, comets and interstellar dusts. Inside these meteorites, there’s numerous amino acids. This life’extraterrestrial origin lets think that it could exist somewhere else.
Theory of the impact of the meteorites of extraterrestrial origin
Life would have been born in the abysses of the sea, next to hydrothermal chimneys which reject molecules, which, transformed, allow syntheses of organic molecules and amino acids.
The theory of the hydrothermal sources (springs)
Life would have apeared 3,8 - 3,5 billion years ago. There are 3 main theories for its appartion:
The three main hypothesis of the apparition of life on earth:
The bacteries and micro-organisms:
at the beginning of life
